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Trickle recoveries aren’t recoveries

Posted by Preston on 2009-09-25

In environments with satellite offices, a common “backup” technique described in a lot of situations is what I’d generically call a “trickle backup” technique. This uses either some form of asynchronous replication (either block or file), or some other state of file/block deduplication, etc., to achieve very small backups (after the first) back to a central site.

These are inevitably done for one or both of the following two reasons:

  1. Staff at the satellite office do not have the technical skills to manage local media or backup storage nodes/media servers.
  2. The WAN bandwidth is too little (or too costly) to do full-scale backups.

Remembering my definition of recoverable in The 7 Procedural Obligations of Backup Administrators, I’d like to suggest that for most situations, there’s no such thing as a trickle recovery. To reiterate, my definition of recoverable is:

  1. The item that was backed up can be retrieved from the backup media.
  2. The item that is retrieved from the backup media is usable as a replacement to the data that was backed up.
  3. The item can be retrieved within the required window.

Trickle backups, if not considered properly, cease to be valid backups if they violate item 3 above.

Whenever trickle backups are considered, there must be rigorous planning conducted (including discussions with appropriate stakeholders) to determine what recovery methods will be considered valid. Let’s discuss briefly what might need to be considered:

  1. Will individual file level recovery back across the WAN connection be possible?
  2. What will be the maximum amount of data that can be recovered across the WAN connection?
  3. How will larger data recoveries be facilitated?
  4. How will complete system recoveries be facilitated?
  5. Can all recoveries be completed within SLAs?
  6. Are HR and IT policies in place to prevent situations where satellite office recovery requirements may be abandoned or delayed due to staff shortages or local workloads?

If all 6 of those questions don’t have answers that are compatible with SLAs and business requirements, then there is no valid satellite backup system in place.

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